Gas separation membrane modules have been used in various applications because they are small and can easily separate gases by simple operation in comparison with other separating means. Gas separation can be conducted by introducing a mixed gas into a gas separation membrane module where the gas is separated into a permeate gas which has permeated the membrane and a non-permeate gas which has not permeated the membrane. The interior of the gas separation membrane module is partitioned into two spaces by the gas separation membrane. Since a gas flow rate through the gas separation membrane is proportional to a pressure difference between these two spaces (a partial pressure difference for each gas component), the mixed gas fed to the gas separation membrane module is generally pressurized.
A shell feed type gas separation membrane module, that a mixed gas is fed into the outer space of a hollow fiber membrane (gas separation membrane) in a vessel while gas separation operation, exhibits excellent pressure capability. Thus, a shell feed type gas separation membrane module can be suitably used for gas separation, particularly by feeding a high-pressure mixed gas. Patent Reference 1 has disclosed an example of a conventional shell feed type gas separation membrane module.
We will describe a gas separation membrane module disclosed in Patent Reference 1 with reference to FIG. 11.
A gas separation membrane module shown in FIG. 11 comprises a hollow fiber element and a vessel having vessel body 103 housing the hollow fiber element and lid 104. The hollow fiber element has a number of hollow fiber membranes 101 and tube sheet 102 holding hollow fiber membranes 101 as a bundle. Tube sheet 102 is a member made of, for example, an epoxy resin, which holds hollow fiber membranes 101 by embedding one ends of hollow fiber membranes 101 such that hollow fiber membranes 101 penetrate tube sheet 102 in its thickness direction and the open-end face of hollow fiber membranes 101 are exposed from tube sheet 102.
Vessel body 103 is a tubular member having an open end to which tube sheet 102 of the hollow fiber element is attached. For attaching tube sheet 102 to vessel body 103, one end of vessel body 103 has a concave portion. Tube sheet 102 is equipped with annular member 150 for holding tube sheet 102 in the concave portion and then fitted into the concave portion, over which lid 104 is attached to vessel body 103. Thus, the peripheral edge of tube sheet 102 is sandwiched between annular member 150 and vessel body 103 for holding.
The high-pressure mixed gas is introduced into the vessel from a mixed gas inlet (not shown) formed in vessel body 103, and flows along hollow fiber membranes 101 while particular gas components permeate hollow fiber membranes 101. A gas having not permeated hollow fiber membranes 101 is discharged from the vessel via a non-permeate gas outlet (not shown) formed in vessel body 103. On the other hand, a gas having permeated hollow fiber membranes 101 is discharged from permeate gas outlet 104a formed in lid 104 via the open ends of hollow fiber membranes 101 and a permeate gas flow path between tube sheet 103 and lid 104.
During gas separation using the above gas separation membrane module, tube sheet 103 is under a high pressure toward lid 104. Thus, the gas separation membrane module has breathable holding member 151 between lid 104 and tube sheet 102, and holding member 151 supports tube sheet 102 on the side facing lid 104, to prevent damage in tube sheet 102 due to a pressure.
However, a high-pressure gas may be introduced from permeate gas outlet 104a into the gas separation membrane module, for example, due to wrong operation, and resultantly, a pressure in the reverse direction that applied during normal operation may be applied to tube sheet 102. Tube sheet 102 is just supported by the peripheral part on opposite side to the side supported by holding member 151, and therefore, the pressure in the reverse direction that applied during normal operation to tube sheet 102 may damage tube sheet 102, which may lead to movement of the whole hollow fiber element within the vessel and finally damage hollow fiber membrane 101.
Such a problem might be solved by increase in a thickness of tube sheet 102 to make tube sheet 102 stronger. Increase in a thickness of tube sheet 102, however, reduces an effective area of hollow fiber membranes 101, which leads to reduce gas separation ability of the gas separation membrane module.
Furthermore, as described above, holding member 151 disposed between lid 104 and tube sheet 102 must be breathable. Thus, the gas separation membrane module described in Patent Reference 1 comprises a holding member body 152 having a number of perforations 152a and porous layer 153 intervening between holding member body 152 and tube sheet 102, has a complex configuration. Furthermore, a resin plate (not shown) binds the ends of hollow fiber membranes 101 in the opposite side to tube sheet 102 for preventing them from being loose. When hollow fiber membranes 101 are bundled as described above, the gas separation membrane module must be handled in vertical position because hollow fiber membrane 101 tends to be ruptured in horizontal position.
Patent Reference 1: Japanese published unexamined application No. 1986-57207.